Background

Diplopia is the subjective complaint of seeing 2 images instead of one and is often referred to as double-vision in lay parlance. The term diplopia is derived from 2 Greek words: diplous, meaning double, and ops, meaning eye. Diplopia (double vision) is a common subjective complaint, or diplopia may be elicited during the course of an eye examination. Diplopia is often the first manifestation of many systemic disorders, especially muscular or neurologic processes.[1] An accurate, clear description of the symptoms (eg, constant or intermittent; variable or unchanging; at near or at far; with one eye [monocular] or with both eyes [binocular]; horizontal, vertical, or oblique) is critical to appropriate diagnosis and management.[2, 3]

Binocular diplopia occurs only when both eyes are open and can be corrected by covering either eye. Monocular diplopia persists in one eye despite covering the other eye and can usually be corrected by using a pinhole. Monocular diplopia can be unilateral or bilateral. Physiologic diplopia is a normal phenomenon depending on the alignment of the ocular axes with the objects of regard (eg, focusing on a finger held close results in distant objects being blurry but double).

Polyopia refers to the perception of more than 2 images and is often a monocular phenomenon caused by refractive aberrations resulting in multiple images of one object. In such cases, the dominant image of the object of regard is accompanied by secondary images that may be less intense, distorted, or fleeting. Causes of polyopia include irregular corneal astigmatism, lenticular opacities, multifocal lenses, and corneal rings of significantly different focality within the pupil created by refractive surgery or contact lenses. Cerebral polyopia however can also occur and typically produces bilateral, simultaneous, and symmetric polyopia.

Animal models

Unless the visual fields of the eyes overlap, binocular diplopia cannot occur. Among vertebrates, the potential for diplopia (and for stereoscopic depth perception) depends on where the eyes are located in the head. Eyes located on either side of the head provide a wide visual field but with a less overlapped visual field. These animals have less field for binocular vision and less risk for diplopia when one eye becomes misaligned. However, when both eyes are located in the front of the head, a greater visual field overlap exists and, thus, a better binocular depth perception, as frequently seen in predators. Misalignment of such eyes may result in diplopia.

The eyes of birds demonstrate many unique anatomical features, one of which is the presence of multiple foveae and, in some cases, a streak fovea linking 2 foveae. Thus, they may be able to have 2 separate areas of regard without disabling diplopia. How the visual perception occurs in these cases remains debatable.

Pathophysiology

Binocular diplopia (or true diplopia) is a breakdown in the fusional capacity of the binocular system. The normal neuromuscular coordination cannot maintain correspondence of the visual objects on the foveae of the 2 eyes. Rarely, fusion cannot occur because of dissimilar image size, which can occur after changes in the optical function of the eye following refractive surgery (eg, LASIK) or after a cataract is replaced by an intraocular lens or because of aniseikonia, which represents a discrepancy in image size perceived by the two eyes.

The distortion of one image may be interpreted as diplopia by the patient; however, the same object does not appear to be in 2 places but rather appears differently with each eye.

Monocular diplopia may result from abnormal light transmission to the retina (eg, corneal distortion or scarring, multiple openings in the iris, cataract or subluxation of the natural lens or pseudophakic lens implant, vitreous abnormalities, retinal conditions). Monocular diplopia must be distinguished from metamorphopsia, in which objects appear misshapen.

Epidemiology

Frequency

United States

No figures are available as to prevalence of diplopia in the United States.

International

International incidence rates of diplopia are unknown. The incidence of diplopia as a chief complaint in emergency departments is low. One study of a specialist eye hospital in London, United Kingdom, reported the incidence of diplopia as the chief complaint in only 1.4% of the presenting cases.[4]

Mortality/Morbidity

Divergent pathological processes, each with its own morbidity and mortality, can cause diplopia. However, irrespective of cause, diplopia has significant morbidity in terms of difficulty with depth perception and confusion with orientation of objects, especially when performing visually demanding tasks, such as driving a vehicle or operating tools. Therefore, in assessing visual disability after injuries, loss of binocularity accounts for a major percentage of loss of function.

Race

No information is available regarding differences in various racial groups.

Sex

No information is available suggesting differences in prevalence with respect to sex.

Age

Diplopia is encountered almost exclusively in adults or in those with mature visual systems because of their inability to ignore the second image.

Young children may not be able to express this symptom. More importantly, the immature visual system deals with diplopia by suppressing the poorer image, possibly resulting in irreversible amblyopia. Children with obvious and marked ocular malalignment from strabismus are comfortable and content because the visual image from the deviating eye is suppressed and not noticed.

History

A clear and comprehensive history is the single most useful evaluation in treating patients with diplopia. The patient typically presents with a history of double vision, where single objects appear as double. Specific inquiry as to onset, progression, effects of distance of target, and variability with head posture or gaze direction, as well as previous similar episodes (especially if associated with other neurologic symptoms) and/or spontaneous resolution, is very helpful in the diagnosis and management of diplopia.

Three important symptoms should be elicited, as follows:

Does covering either eye make the diplopia disappear? This test helps to rule out monocular diplopia, which persists in one eye even if the other eye is covered.

Is the deviation the same in all directions of gaze or by tilting and rotating the head into different positions? This suggests a comitant deviation, with no difference in separation of the images in all directions of gaze. When the extent of deviation changes (and indeed possibly disappears in a given direction), then the deviation is incomitant and suggests a problem with innervation, most likely a paretic muscle.

Is the second object displaced horizontally (side-by-side images) or vertically (images above each other)? Oblique diplopia (images separated horizontally and vertically) should be considered as a manifestation of vertical diplopia.

The traditional and detailed evaluation of the chief complaint includes onset (abrupt or slow), severity, duration, location, associated symptoms, and aggravating and relieving factors. A comprehensive and complete review of all these aspects, if necessary with a questionnaire, is more important than the appropriate physical examination or special tests.

Other significant aspects include a review of systems (eg, history of diabetes, vascular disease, or hypertension; headache and other neurologic complaints; muscle fatigue or weakness; medications and drugs being used[5] ), as well as a past medical and surgical history.

Inquire about recent trauma to the face and the head. Blunt injury to the cheek can result in a blow-out fracture of the orbit with hematoma or entrapment of the soft tissues and extraocular muscles, restricting upward and downward eye movement. Entrapment of the inferior rectus muscle can be confirmed by a forced duction test. Blunt head injury may also be associated with nonspecific sixth cranial nerve (abducens) weakness and severe diplopia when gazing to the affected side.

Physical

The first aspect of the physiologic evaluation includes the sensory component.

Confirm that the symptom is monocular or binocular. Does covering each eye in turn alleviate the problem, or does the diplopia persist despite covering the "good" opposite eye? Monocular diplopia is very uncommon. Possible causes include severe corneal deformity or marked astigmatism (keratoconus), multiple pupils or openings in the iris, refractive anomalies within the eye (early cataracts or partially displaced lenses as in Marfan syndrome), as well as retinal abnormalities (macular scarring and distortion).

Evaluate the magnitude of difference in spectacle correction required for each eye. Marked differences between the eyes (anisometropia) will frequently produce disabling diplopia, especially in extremes of gaze.

Determine the visual acuity in each eye separately, with and without spectacle correction and with a pinhole. Does a pinhole improve the visual acuity, or does it improve monocular diplopia? Major improvement in visual acuity with a pinhole suggests intraocular or refractive problems.

Evaluate the visual field by confrontation testing or formal visual field mapping to detect possible space occupying masses impinging on the visual pathways and/or cranial motor nerves. With severely constricted fields, the peripheral clues for fusion may be lacking, resulting in diplopia.

Determine how various directions of gaze modify the diplopia. Is the diplopia the same in the 9 cardinal directions of gaze? This includes straight ahead (primary gaze), to each side as well as up and down while looking toward that side, and straight up and down from the primary position. This evaluation can enhance subtle weaknesses of individual muscles that may not be apparent during testing of the range of movements.

Evaluate how tilting the head to the left or to the right alters the diplopia. The double vision will increase when the head is tilted to the same side if vertical diplopia is present due to weakness of the superior oblique muscle (innervated by the fourth cranial nerve [trochlear nerve]). Eliciting increases or decreases in the separation of the 2 images is an essential part of the Park three-step test.

The motor aspect of the physiologic evaluation includes the following:

Determine the existence of a normal range of ocular movements. First observe each eye separately (ocular ductions), and then observe both eyes together (ocular versions). Careful consideration of the extraocular muscle anatomy clarifies the effect of each muscle and why one direction of gaze isolates each muscle's effects.

Determine that each eye is able to fully adduct (turn inward) and abduct (turn outward) and to fully elevate and depress in abduction and adduction (as if the eye is tracing a capital letter "H").

This helps to determine which eye muscle is responsible for diplopia; normal contraction of the medial rectus muscle produces adduction, while abduction is caused by the lateral rectus muscle. Because the vertical eye muscles diverge from their origination at the apex of the orbit to the insertion on the globe, the superior and inferior recti muscles can be evaluated best with the eye abducted.

With the eye abducted, the eye will move down by the inferior rectus muscle, while the superior rectus muscle will move it upward in abduction. Likewise, the oblique muscles can be isolated with the eye adducted; with the eye turned in, the inferior oblique muscle elevates and the superior oblique muscle depresses the eye. A simple rule for superior oblique weakness is "the eye that is looks highest in adduction is pointing at the affected superior oblique muscle."

Determine if diplopia worsens when the muscles are fatigued (eg, after strenuous use, at the end of the day). Myasthenia gravis can affect any muscle or group of muscles, and a common presenting symptom is variable diplopia. If myasthenia gravis is suspected, its diagnosis can be confirmed by intravenously injecting a short-acting anticholinesterase (ie, 10 mg/mL edrophonium chloride [Tensilon]). See Other Tests.

Determine that other ocular motor functions are normal, as follows:

Is the lid in a normal position?

Is the pupil response normal and symmetric with the other pupil? Pupil asymmetry is a sinister sign when associated with diplopia because it indicates involvement of the third cranial nerve (oculomotor nerve). An important diagnostic clue is provided by detecting pupil sparing but otherwise complete third nerve palsy (eg, ptosis; inability to elevate, depress, or abduct the eye). A pupil whose function is spared, particularly if associated with complaints of headache or pain around the orbit, suggests diabetic third nerve palsy. This can avoid expensive and unnecessary imaging studies. Complete and spontaneous recovery after approximately 6 weeks is virtually the rule. Similar temporary mononeuritis multiplex processes can affect the sixth cranial nerve (abducens) with temporary loss of abduction.

The anatomical evaluation includes inspection, palpation, percussion, and auscultation.

Inspect the head position, eyes, eyelids, orbits, and face for symmetry or displacement (upward, downward; proptosis, enophthalmos). Ptosis of the upper eyelid indicates possible third nerve lesions, while eyelid retraction suggests thyroid ophthalmopathy. Abnormal head position (especially tilting the head to one side) suggests superior oblique muscle palsy.

Note inflammation or vascular congestion that may be suggestive of orbital cellulitis, orbital tumors (rhabdomyosarcoma), arteriovenous malformation (carotid cavernous fistula), and thyroid ophthalmopathy. Palpate the orbital rim for fractures and any absences (eg, encephalocele). Palpate soft tissues surrounding the eye for tumors. Gently push on the closed eyelid to determine increased resistance (fullness of the orbit), comparing one eye to the other eye. This may disclose orbital disorders (eg, fractures, tumors).

Causes

Binocular diplopia caused by ocular misalignment can stem from supranuclear disease, nuclear disease, or infranuclear disease, which includes disease of the extraocular muscles, the nerves innervating these muscles, or the neuromuscular junction connecting the nerve and the muscle. It can be further classified as intermittent or constant. Common causes include the following:

Imaging Studies

Evaluate old photographs to determine if a head posture (if present) is long-standing. Commonly, a congenitally weak superior oblique muscle can be compensated for by head tilt, but osteoarthritis of the neck or other mechanism can result in decompensation and sudden symptoms of a chronic subclinical condition.

Order CT scan or MRI (with contrast) of the skull and orbits to rule out intracranial masses or other pathologic processes, such as the following[7] :

Carotid cavernous fistula: Angiography may be required to confirm the presence of a low-flow fistula.

Disease of sinuses (eg, infection, tumor) or bony disorders (eg, dysostoses, encephalocele) can account for displacement of the eye.

Traditional guidelines for imaging patients with new-onset diplopia include imaging all patients younger than 50 years with other neurologic findings, with a progressive course of diplopia, or with a history of cancer.[8] For patients older than 50 years, imaging is not always necessary during the initial evaluation. Physicians should conduct a careful review of the patients' history to determine if imaging is medically indicated.

Other Tests

Cover-uncover test

The cover-uncover test can be used to detect heterotropias. The subject fixates on an object while one eye is covered. If the uncovered eye adducts, the eye has exotropia; if the uncovered eye abducts, the eye has esotropia; if there is upward movement, it has hypotropia; if there is downward movement, it has hypertropia.

If the patient has tropia, the ocular deviation can be measured with prisms. Prisms of differing strengths can be placed in front of the uncovered eye. Prisms of increasing strengths are tested until there is no longer a deviation noted in the uncovered eye.

Tensilon test

The edrophonium (Tensilon) test can be performed exclude myasthenia gravis.

Intravenous injection of a short-acting anticholinesterase (ie, 10 mg/mL edrophonium chloride [Tensilon]) should be part of the initial workup of a patient with diplopia. Draw up 1 mL, and establish venous access. Then, inject a test dose of 1 mg intravenously to exclude possible hypersensitivity; if no adverse effect is evident, inject the remaining 9 mg.

The expected (normal) cholinergic response includes salivation; lacrimation; flushing; and a brief, but often quite dramatic, reversal of muscle weakness with temporary correction of diplopia and/or ptosis. Occasionally, an excessive cholinergic response may result in increased vagal tone with serious bradyarrhythmias; atropine (0.5 mg) should be available as an antidote.

Other myopathies (eg, progressive external ophthalmoplegia, myotonia) do not respond to anticholinesterases.

The Tensilon test has been largely supplanted in the clinic by safer and less-invasive clinical tests (eg, sleep or rest test, ice test).

Forced duction test

If a lack of movement of one eye occurs in a given direction, excluding a tethered (or fibrotic) muscle may be helpful. Evaluate whether the globe can be passively moved toward the affected area. Traditionally, a forceps is used (after topical anesthesia) to grasp the limbus, and then the eye can be gently tugged in the desired direction. It may be possible to achieve the same result less traumatically by using a cotton wool bud (soaked in topical anesthetic) to "push" on the limbus in the desired direction.

Lee or Hess screen

This highly specialized test separates the field of vision of the 2 eyes. With one eye, the subject fixates on the corners of a rectangle. The other eye is used to visualize the placement of a marker on the same location. Any overaction or underaction will become evident; when one eye has a weak muscle, it will not move as much as the other eye. However, if that eye is used to fixate, the excessive stimulation required will result in an overshoot of the normal yoke muscle in the opposite eye.

Park three-step test

The Park three-step test can help elucidate which of the 4 extraocular muscles responsible for vertical eye movements are responsible for a vertical diplopia. Although first appearing impossibly complex, this test follows a logical progression to progressively eliminate groups of muscles from the 4 pairs.

First, determine which eye appears higher with the head in a normal position. Then, determine which eye is higher with gaze to the left or to the right (ie, with the head turned to the right and then turned to the left). Lastly, determine which eye is higher with the head tilted left and tilted right. (The patient can also help by commenting about when the diplopia is worse.) Then, answer the questions in the following steps:

Step 1: Is the left eye or the right eye higher in primary gaze? This reduces the possibilities of muscles from 4 pairs to 2 pairs. For example, if the right eye is higher, the weakness resides either in the muscles depressing the right eye (right superior oblique muscle and right inferior rectus muscle) or in the elevators of the left eye (left superior rectus muscle and left inferior oblique muscle).

Step 2: Is the deviation greater with left head turn or with right head turn? This step reduces the alternatives to only one pair of muscles. If the right eye deviates most when the head is turned to the right (both eyes are turning to the left), then only the right superior oblique muscle or the left superior rectus muscle remains.

Step 3: Is the deviation greatest with tilting the head to the left or to the right? Called the Bielschowsky head tilt, it relies on the torsional balancing reflexes provoked by head tilt. The higher eye extorts (because of the inferior oblique muscle), while the lower eye intorts (because of the superior oblique muscle).

By combining steps 1-3, only one muscle remains as the culprit. This test requires a logical analysis and the exclusion of alternative possibilities. However, the astute clinician can greatly simplify this process by recognizing that the superior oblique muscle is by far most likely to be responsible for a vertical diplopia. A head tilt to the same side as the involved muscle exacerbates the problem. A very simple rule of thumb is that "the eye that is highest in adduction looks at the affected muscle."

The severity of the diplopia can be quantified by plotting the field of single binocular vision on a Goldmann perimeter (when available) or by using either a device to standardize the head position or a questionnaire.[9, 10]

The questionnaire assigns a score of 6 if the diplopia is always present straight ahead, a score of 4 if the diplopia is present in the down, right, left, and reading position, and a score of 2 if the diplopia is present in upgaze. The scores are halved if the diplopia is sometimes present in these gaze directions.

Single-Fiber Electromyography

Single-fiber electromyography (EMG) can be used to detect myasthenia gravis in seronegative cases with isolated ocular findings. Single-fiber EMG is a highly sensitive test for detecting defects in the neuromuscular junction. An electrode measures the potentials of different muscle fibers that are innervated by the same nerve. In a healthy individual, the action potential will excite the muscle fibers at the same time. If there is pathology, there will be variability in the time of excitation of the muscle fibers. Jitter represents the difference in time between the depolarization of the two muscle fibers and is increased in those with myasthenia gravis. The threshold for an abnormal test result is a jitter value greater than the upper limit of the normal value for the specific muscle or greater than 10% of muscle pairs tested with increased jitter.[11]

Medical Care

Patching one eye: Patching is often required, since the patient has to continue functioning while awaiting resolution or intervention.[12]

Stick-on occlusive lenses can be applied to glasses to minimize the cosmetic handicap of a patched eye, while sufficiently blurring the one eye to minimize disabling double vision.[12]

Fresnel prisms: These prisms can be stuck to glasses.[12] Although these prisms are only appropriate if a stable deviation is present across all directions of gaze, they severely blur the image from that eye and function in many ways like an occlusive lens.

Treatment of myasthenia gravis: Mestinon or other long-acting anticholinergic agent, as well as corticosteroids, may be required.

Orthoptic exercises: In healthy individuals, convergence exercises have been proven via randomized controlled trials to reduce symptoms of convergence insufficiency.[13] Orthoptic exercises have also been shown to improve surgical outcomes in patients with strabismus and can be considered as adjunctive treatment to surgery in patients with intermittent exotropia.

Surgical Care

Strabismus surgery is occasionally necessary.[12] The typical recession/resection is rarely indicated due to the one muscle often being permanently weak, and any standard surgery will lose effect over time. Exceptions include a blow-out fracture when the release of the entrapped soft tissues from the fracture in the floor of the orbit can be very effective.

Transposition surgery (Hummelsheim surgery): With permanent paralysis of the lateral rectus muscle, overcoming the unopposed tone of the medial rectus muscle is possible by splitting the superior and inferior recti muscles and by reinserting the lateral half of each muscle at the lateral rectus insertion. Otherwise, any recession of the medial rectus muscle will be of only temporary benefit. Despite achieving single vision straight ahead, the diplopia will persist with gaze toward the paralytic muscle.

Knapp superior oblique muscle paralysis: With permanent weakness of the superior oblique muscle, it is possible to weaken the yoke muscle of the opposite eye (superior rectus muscle) as well as the direct antagonist (inferior oblique muscle) in the same eye, together with a shortening of the affected muscle, to minimize the deviation.

Chemodenervation[12] : This helps prevent the contracture in eyes with extraocular muscle paresis, especially when return of function is expected. Multiple injections over several months of botulinum toxin into the medial rectus muscle reduce contracture due to a weak lateral rectus from a sixth nerve paralysis. The effect may be more permanent than expected; the opposing un-injected muscle may develop a degree of permanent shortening and contracture.

Patient Education

Patients must be educated on the importance of determining the exact cause of diplopia, since some conditions responsible for diplopia may be very serious. Otherwise, a clear explanation of the condition, its natural history, alternative options, and general prognosis will alleviate patient concerns and motivate perseverance.[14]

Specialty Editors

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Andrew G Lee, MD, Chair, Department of Ophthalmology, Blanton Eye Institute, Houston Methodist Hospital; Clinical Professor, Associate Program Director, Department of Ophthalmology and Visual Sciences, University of Texas Medical Branch School of Medicine; Clinical Professor, Department of Surgery, Division of Head and Neck Surgery, University of Texas MD Anderson Cancer Center; Professor of Ophthalmology, Neurology, and Neurological Surgery, Weill Medical College of Cornell University; Clinical Associate Professor, University of Buffalo, State University of New York School of Medicine

Disclosure: Received ownership interest from Credential Protection for other.

Acknowledgements

Izak F Wessels, MBBCh, MMed, FRCSE, FACS is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, American Medical Association, and Royal College of Surgeons of England